Processes for the simultaneous displacement of petroleum and water in formations



y 1969 w. B. GOGARTY ETAL 3,443,635

PROCESSES FOR THE SIMULIANEOUS DISPLACEMENT OF PETROLEUM AND WATER INFORMATIONS Filed Sept. 6, 1967 Sheet 1 of s FIGI FIGZ 0'8 SAMPLE#2291914 08 SAMPLE Z-lfiZMd 0.7 0.7

WA TEE WATE/i 0 IO 4o 50 e0 70 a0 90 100 0 IO 20 30 e9 70 so 90 I00 s w.PORE VOLUME) I s PORE VOLUME) FIG?) FIG4 SAMPLE 3-370 Md SAMPLE 4-l5/ Md0.7 0.7

0.6 0.6 Kr Kr Oi DJ .0 0.0 0 IO 20 30 4O 5O 6O 70 80 90 O0 0 I0 20 3O 4O5O 60 I00 8 PORE VOLUME) 5 PORE VOLUME) INVENTORS 8. 6064/? TY RELATIVEMOBILITY (l/cp) y 1969 w. a. GOGARTY ETAL 3,443,635

PROCESSES FOR THE SIMULTANEOUS DISPLACEMENT OF PETROLEUM AND WATER INFORMATIONS 2 Filed Sept. 6, 1967 Sheet of 3 SAMPLE 229 TOTAL RELATIVEMOBILITY (I/cp) IO 3o so so so I00 WATER SATURATION PORE VOLUME IMIN/MUM mmL RELATIVE MOBIL/T) U6 LE 0/L 5L .02- some -A .oos-

00 I I I I I I I I I .IO .20 40 .so [.0 2.0 4.0 6.0 IO 20 40 so I00FRONTAL VELOCITY (ft. Idoy) M/VE/VTORS W/LL/AM E. GOGARTY HAROLD MEABONMay 13, 1969 w. B. GOG ARTY ETAle 3,443,635 PROCESSES FOR THESIMULTANEQUS DISPLACEMENT OF PETROLEUM AND WATER IN FORMATIONS FiledSept. 6, 1967 Sheet 3 or 3 FIG. 3

Obtain oil relative permeability and water relative permeability of eachsample Calculate total relative mobility vs water saturation for eachsample For primary and secondary or, For tertiary recovery) lessdesirably for tertiary) m l m l Minimum mobility for any and all Runtransient reservoir tests to determine samples water relativepermeability Select most appropriate relationship from IL above (Fig'.4)

Minimum mobility from relationship selected mb Fig.5 l

Design displacement fluid having a mobility, less than the minimum totalrelative mobility as determined above LDesign Buffer Fluids 1 7 llnject, controlling frontal velocities 1 MII E/VTORS' WILLIAM B GOGARTYHAROLD I? MEABO/V United States Patent O US. Cl. 166252 26 ClaimsABSTRACT OF THE DISCLOSURE Petroleum and water can be simultaneouslydisplaced in formations by determining the oil relative permeability andthe water relative permeability both in relation to water saturation ofrepresentative rock samples, then calculating the total relativemobility and determining the minimum total relative mobility reasonablylikely to be encountered in the formation. A displacing fluid having amobility not greater than the minimum total relative mobility can thenbe injected into the formation to simultaneously displace, at controlledrate, water and petroleum present in the formation. In tertiaryoperations transient testing may be utilized in the determination of theminimum total relative mobility. Petroleum is obviously used forlubricating oils, gasolines, coke, etc.

CROSS REFERENCES TO RELATED APPLICATIONS The present invention issimilar in purpose, but somewhat ditferent in technique from S.N.665,845 filed Sept. 6, 1967 by William B. Gogarty and assigned to theassignee of the present invention.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to the field of miscible displacement of petroleum and waterfrom formations. The invention has use in the secondary and also in thetertiary recovery of petroleum from formations. The invention is alsousful in cases in which it is desirable to either speed primaryproduction or to enhance a weak natural gas or water drive duringprimary production. The invention may also be utilized to displacefluids from around well bores, e.g. in modifying the injectivitycharacteristics of wells and in other well bore treating operations.

Description of the prior art Various flooding methods for thedisplacement of petroleum in formations have been developed in the past.These include water floods in which water is injected into the formationto displace oil; thickened water floods in which polymers, e.g. certainpolyacrylamides; carboxymethyl celluloses, etc. are used to decrease themobility of the water and somewhat control the fingering generallyencountered in ordinary water floods; alcohol floods; emulsion floods;e.g. US. 3,208,515 and US. 3,261,399; and the relatively new developedsoluble oil types of flooding media and processes, e.g. US. 3,254,714and 3,275,075.

As is well known, the total relative mobility of two phases (e.g. oiland water), M flowing in porous petroleum bearing formations is relatedto both the viscosities of the fluids in place, and also to thecharacteristics of the individual formation in question, according tothe following general formula:

l'o l'w M o-w w where: k is the relative permeability with respect tooil,

3,443,635 Patented May 13, 1969 k, is the relative permeability withrespect to water. no is the viscosity of oil. ,u is the viscosity of thewater.

The relative permeabilities, k and k vary due to variations in watersaturation, S and rock characteristics from point to point in mostreservoirs. Various calculation methods have been suggested for dealingwith the individual mobilities of oil and water and their ratios, e.g.those for water flooding discussed in Secondary Oil Recovery by C. R.Smith, Chapter 7, pp. 183-235 (Reinhold, 1966) This same text alsodiscusses various methods of miscible flooding and gives methods for thedetermination of performance of some such miscible floods, e.g. as atpages 357-358.

Most of these calculational methods have been useful for the predictionof recovery rather than for the optimizing of the displacing fluids. Inpractice, most past flooding operations have not involved simultaneousdisplacement of water and oil and have merely attempted to keep theviscosity of the flooding agent above that of the oil in place. To thebest of our knowledge, no successful method of optimum slug designadaptable to a variety of reservoirs and to a variety of displacingfluids which are capable of simultaneous displacement of water and oilhas previously been available.

SUMMARY OF THE INVENTION The present invention affords new methods forthe displacement of petroleum in formations which utilize displacementfluids specifically designed according to new techniques for theoptimizing of the displacement fluids to obtain substantially maximumoil recovery without excessive fluid component or pumping costs due tounnecessarily high viscosities of the displacing fluids.

In preferred embodiments, the present invention simultaneously displacesboth water and oil in the formation and maintains the total relativemobility of both of the displaced fluids greater than that of thedisplacing fluid so as to substantially avoid instability under theconditions which are reasonably likely to be encountered in thereservoir.

It is known that the water relative permeability, k and the oil relativepermeability, k vary with water saturation S in such a manner that aswater saturation increases the relative permeability to water k,increases While the relative permeability to oil k decreases (see, forexample, FIGURES 1 to 4). Since the viscosities of the oil and water ,uand a respectively are relatively constant within the reservoir, thetotal relative oil and water mobility, M, in relation to watersaturation, reaches a minimum point. That is, starting at a low value ofwater saturation S M,, will first decrease as S increases, and thenreach a minimum point and thereafter increase as S increases (see, forexample FIGURE 5). The present invention therefore utilizes, in certainof its preferred embodiments, the finding that, generally speaking, forany given point in a reservoir containing oil and water, there exists aminimum total relative oil and water mobility M By finding this minimumby determining the k and k for each of a number of rock samples takenfrom different points in a reservoir, then selecting the lowest of theseminimum values, a minimum total relative oil and water mobility M,, maybe found for any given entire reservoir or portion of a reservoir. It ismost important to the present invention that this minimum value to beencountered in the reservoir may be determined without knowing the watersaturation at various points Within the reservoir. Water saturation atpoints ahead of the displacing fluid is affected by the displacementprocess and is, at best, extremely difficult to estimate prior to theinitiation of flooding.

Of course, the minimum total relative oil and water mobility M,,reasonably likely to be encountered in the reservoir may be determinedfrom the minima of the various rock samples by the application ofstatistical sampling techniques so that the minimum may be selected withvarioss degrees of confidence. Where the taking and testing of a largenumber of rock samples indicates that the reservoir is relativelyhomogeneous and that the samples may be taken as representative of thereservoir as a whole, the minimum total relative oil and water mobilityas determined from the lowest sample tested may be taken as the minimumfor the entire reservoir. Alternatively, it may be found on the basis ofexperience in particular reservoirs, that the assigning of a factor,e.g. 90% of the lowest total relative oil and water mobility encounteredin any sample of a set of samples, provides a mobility having a highdegree of confidence that it will not be subceeded at any point in thereservoir. Such experience may permit finding the minimum M for anentire typical reservoir on the basis of even a simple representativerock sample.

Regardless of the method used for determining, with a desired degree ofcertainty, the minimum total relative oil and water mobility to beencountered within the reservoir, the present invention permits suchdetermination to be made purely from rock and oil and water sampleswithout knowledge of the water saturation at various points within thereservoir during flooding. The present invention then utilizes thisminimum total relative oil and water mobility, M., as the criteria forthe selection or designing of the displacement fluid. Knowing theminimum M to be encountered, and having rock specimens at hand, adisplacing fluid, e.g. an alcohol, ketone, aldehyde, soluble oil, orother displacing fluid can be selected to have a mobility less than saidminimum total relative mobility to be encountered in the fluids beingsimultaneously displaced and therefore instabilities can besubstantially avoided.

The techniques of the present invention are particularly important withthe new micellar and other multi-component displacement fluids whichpermit careful tailoring of the mobility of the fluid to virtually anydesired value. In most such composite fluids there will be a number offormulations which will meet the requirement of not exceeding the totalrelative oil and water mobility. From these can then be selected themost economic fluid with respect to the cost of its ingredients and thecost of injecting the fluid and moving it through the reservoir. Thiseconomic optimization may be readily conventionally accomplished basedon the well spacing, formation thickness, oil in place and other factorsto be encountered in the reservoir.

Where relatively expensive high efiiciency displacement fluids are beingutilized, e.g. soluble oils, it will generally be desirable to drive abank or slug of such displacement materials with a secondary fluid orfluids, e.g. water or water separated from the slug by a mobilitybuffer, e.g. thickened water or water external emulsion. Since fingeringof such secondary fluids through the first bank of high eificiencydisplacement fluids would seriously detract from the efliciency of thetotal flooding operation, it is especially desirable that the mobilitiesof such buffer fluids be maintained below the mobilities of thedisplacement fluids which they drive. In short, according to the presentinvention, any number of fluid banks may be injected sequentially, eachdriving against the one previously injected; so that each (excluding thedrive water which is injected last) can have a lower mobility than doesthe fluid which it drives at the worst point in the reservoir, that is,the point where the total relative oil and water mobiliy reaches aminimum. The mobilities will preferably be measured at substantially theworst (highest) frontal velocities to be utilized during the injectionand recovery process.

Frontal velocities which will be encountered only in relatively smallareas of the formation, e.g. near the well bore can be disregarded wherewarranted by engineering judgment.

Though not absolutely necessary this designing can preferably beaccomplished by simply plotting the mobilities of the variousdisplacement banks (as the ordinate) versus the frontal velocities inthe range anticipated (as the abcissa) and drawing the minimum totalrelative oil and water mobility M,, determined as discussed above, as astraight line parallel to the abcissa (see, for example, FIGURE 6). Thevarious displacement fluids and mobility buffers are then designed toeach have a mobility at each frontal velocity which is less than that ofthe mobility of the preceding fluid at that frontal velocity.

All of the above discussions are based on removal of rock samples fromthe formation and laboratory determination of the oil relativepermeability and water relative permeability by testing such samples. Ingeneral, this method will be preferred for primary and secondaryrecovery and for well treatment operations, but will be less desirablefor tertiary recovery.

A particularly preferred method of the present invention for use intertiary recovery operations is the determination of water relativepermeability by transient reservoir testing. As is known, such transientreservoir testing gives results which are indicative of the entirereservoir. This type of testing can be accomplished by either injectinginto (or possibly withdrawing from) the reservoir, water at a constantrate with the bottom hole pressure of the well being determined as afunction of time.

The geometrical consideration of appropriate plots of the pressureversus time allows determination of a dimensionless group containing thewater permeability at residual oil. (See, e.g. Formation Evaluation, Ed.I. Lynch, Harper and Row (1962) pages 284-318.)

Having run transient reservoir tests with water, the determined waterpermeability (generally expressed in millidarcies) is divided by therock permeability (measured at 100% liquid saturation) expressed in thesame units to arrive at the water relative permeability for thereservoir. Then by referring this value to the values of waterpermeability at water saturations which correspond to zero oil relativepermeability (for example, as in FIGURES l, 2, 3, and 4) the appropriatepair of relative permeability curves can be selected.

In short, this procedure uses transient reservoir test data to selectfrom relative permeability curves, the one most representative of thereservoir. As before, in the selection of the rock sample having theminimum total relative water and oil mobility, various statisticalsampling techniques or an arbitrary or other factor, can be utilized inorder to determine the minimum m0- bility reasonably likely to beencountered in the reservoir. The slug, or bank of displacing fluid canthen be designed to have a mobility less than this minimum valueaccording to the procedures described above.

DESCRIPTION OF THE DRAWINGS FIGURES 1 through 4 show plots of relativepermeability, k versus water saturation S with oil and waterpermeabilities plotted separately on each graph, and with each graphrepresenting a different rock sample obtained from a single reservoir.

FIGURE 5 is a graph of total relative mobility M,, (expressed inreciprocal centipoises) versus water saturation, S with a separate curvefor each of the rock samples utilized in FIGURES 1 through 4, somewhatextrapalated.

FIGURE 6 is a plot of relative mobility (in reciprocal centipoises)versus frontal velocity (in feet/ day) for each of the following: oiland water; an exemplary soluble oil slug; and an exemplary thickenedwater buffer which con tacts the soluble oil slug.

FIGURE 7 is a block diagram of the steps followed in two preferredembodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Representative rock samples areobtained from a reservoir in which recovery operations are to beconducted. Each of these rock samples is flow tested in the laboratorywith specimens of the formation water and the oil in place. The waterrelative permeability k and the oil relative permeability k aredetermined by conventional laboratory methods. (See e.g. PetroleumReservoir Engineering Amyx Bass and Whiting, McGraw-Hill (1960), pages174-202.) FIGURES 1 through 4 are plots (from four samplesrepresentative of the reservoir rock) of the water relative permeabilityand the oil relative permeability versus water saturation expressed inpercent of pore space for water saturations from about 20 to about 70%,a range which encompasses the water saturations which can be encounteredduring flow in the reservoir.

In FIGURE 7, a block diagram of the steps in two preferred embodimentsof the present invention, the preceding is shown as step I.

The viscosity of the formation water and the oil in place are determined(taking a conservatively high value if these viscosities vary from pointto point in the reservoir). From this and the results of step I above,the total relative water and oil mobility M is calculated in relation towater saturation using the equation given previously in thisspecification. This step is shown as step II in FIGURE 7 and the resultsfor each of the four samples used in step I above is shown as a separatecurve in FIGURE 5.

Example I.Secondary recovery operations In this example, FIGURES 1-5 areused to illustrate the rock properties of a reservoir which has notundergone secondary recovery.

The next step is to choose the minimum value of M,, likely to beencountered in the reservoir. While conventional statistical samplingtechniques may be utilized as mentioned above, to determine this minimumvalue to any desired degree of certainty, in this exemplary situation,the rock samples are assumed to be representative of the formation andthe minimum mobility encountered in the samples taken as a group isreasonably certain to be the minimum mobility to be encountered in thereservoir.

The next step, shown as step III in FIGURE 7, is to select the minimumtotal relative mobility for the lowest of the total relative mobilityversus water saturation curves of FIGURE 5. This value, 0.029 for hepresent embodiment as shown in FIGURE on the curve representing sample4, is the lowest combined water and oil mobility which can reasonably beexpected to be encountered in the reservoir.

The next step, step IV in FIGURE 7, is the design of a displacementfluid which has a mobility lower than the 0.029 minimum total relativemobility determined above in order to assure substantial freedom frominstability in t the flooding operation. In the present embodiment aslug of soluble oil is to be followed by a mobility buffer fluidconsisting of water thickened with certain partially hydrolyzedpolyacrylamides of the sort marketed by the Dow Chemical Company underthe designation Dow Pusher and frequently used in conventional thickenedwater flooding operations. The mobility of the soluble oil displacementfluid is adjusted by varying the composition of the soluble oil by trialand error and repeatedly determining its mobility in a rock sample,preferably in the sample in which the minimum M,, was previouslydetermined. Where the effect of the various ingredients on the mobilityof the soluble oil has been previously studied, empirical charts may bereadily constructed to assist in the design of the soluble oil. Where avariety of soluble oil compositions will all meet the requirement ofmobility less than the above determined total relative water and oilminimum mobility, economic considerations will generally determine theparticular composition to be chosen.

As shown in FIGURE 6, the mobility of the soluble oil bank is determinedat each of the frontal velocities to be encountered in the actualflooding operation. The soluble oil of the present embodiment has acomposition by volume as follows:

Percent Petroleum sulfonate 10.3 Isopropyl alcohol 0.4 Crude columnoverhead hydrocarbons 57.2 Water 32.1

As can be seen from FIGURE 6, the soluble oil is chosen because themobilities on the soluble oil mobility curve are in all cases, less thanthe straight line horizontal and parallel to the frontal velocityabscissa which represents the total relative oil and water minimummobility as determined above. It is permissible that the soluble oilmobility curve eventually rise above the minimum M,, curve so long asthe point of intersection is outside of the range of frontal velocitiesto be encountered in the formation.

Similarly, the thickened water is adjusted to a composition ofapproximately 2400 parts per million by weight polyacrylamide yieldingthe lower curve shown in FIG- URE 6. This curve is also proper inasmuchas it is at all points below the mobility curve for the soluble oildisplacing fluid which will precede the thickened water. If more than atwo bank displacement fluid system is desired, additional banks may bedesigned, each having a mobility curve lower than the fluid previouslyinjected at each frontal velocity to be encountered in the operation,and these can then be followed by drive water.

The soluble oil material is then injected into an injection well locatedin the formation from which the rock samples 1-4 were taken. Thequantity of soluble oil injected will generally be based on the distancewhich the soluble oil slug or bank is expected to displace thepetroleum. Conventional techniques of slug sizing, well spacing, andline drive techniques can be employed with the present invention. Inmost cases, petroleum in place will be displaced toward, and eventuallywithdrawn from, a production well located within the formation.

Example II.-Tertiaray recovery operations In Example II, FIGURES 15 aretaken as illustrative of a reservoir which has previously undergoneextensive waterflood operations.

Referring again to FIGURE 7, Example II is the case of tertiary recoveryoperations in which use is made of transient reservoir tests asmentioned above. From these conventionally conducted transient tests isdetermined the Water relative permeability at zero oil relativepermeability (step IIIa). Note that the water relative permeabilitycorresponding to the actual water saturation of the reservoir would beused if the oil saturation is not residual (that is, if the water floodhad not removed substantially all oil displaceable by water).

'In step II'Ib the Water relative permeability (at zero oil relativepermeability in this Example ill) is used to select the most appropriateof the curves determined in step II just as discussed in the previousembodiment. The curves are selected by examining the value of k at thepoint where k equals zero in each of FIGURES 1 through 4, representingrock samples 1 through 4 respectively. For example, in the presentembodiment the transient reservoir tests of step IIIa determine thewater relative permeability to be 0.2]. at the zero oil relativepermeability point. Thus, FIGURES 1-4 indicate that the curve determinedfrom sample 1 most closely fits the results of the transient reservoirtests and therefore may be taken as being most representative of thereservoir as a whole. It should be noted that interpolation between thevarious sample curves might be useful, or in some cases, it may benecessary to obtain additional rock samples in order to find onesufliciently closely representing the reservoir as a whole.

The next step, shown as step IHc of FIGURE 7, is to take the minimumtotal relative oil and water mobility from FIGURE determined by step IIjust as described in the preceding embodiment and utilizing the curve ofthe sample most representative of the reservoir (or any interpolatedcurve between the samples). This value is thus found to be about 0.067for the curve of sample 1 in FIGURE 5 of the present embodiment.

Thereafter, the design of the displacement fluid step IV of FIGURE 7 isconducted as described in the previous embodiment and so also is thedesign of any mobility buffer fluids which follow the displacement fluid(step V in FIGURE 7).

The injection itself shown as step VI in FIGURE 7 is done according toestablished principals of petroleum well bore treatment and recovery,with care being taken to maintain the frontal velocities of the fluidsat rates in the range of those utilized in the preceding steps.

The present invention should not be limited to the above illustrativeexamples and the claims should be considered as including all of thewide variety of modifications and virations which will be made obviousto those skilled in the art upon a reading of the specification.

For example, fluids for use with the present invention may be thickenedby any of the many known viscosity control agents, including withoutlimitation, partially hydrolyzed polyacrylamides, sugar, glycerin,starches, and carboxymethyl cellulose, so long as these are selected inaccordance with the characteristics of the particular reservoir.

What is claimed is:

-1. A process for the simultaneous displacement of petroleum and waterin formations bearing petroleum and water and having at least oneinjection means in said formation, comprising in combination the stepsof:

(a) determining the oil relative permeability relative to watersaturation of at least one rock sample reasonably representative of thestructure of the formation,

(b) determining the water relative permeability in relation to watersaturation of such samples,

-(c) calculating the total relative mobility of water and oil inrelation to water saturation for each such sam- P (d) determining fromthe mobilities of said samples the minimum total relative mobilityreasonably likely to be encountered in the formation,

(e) preparing a displacing fluid having a relative mobility not gearterthan said minimum total relative mobility under the conditionsprevailing in the formation, injecting said displacement fluid into saidat least one injection means so as to simultaneously displace water andpetroleum present in the formation, said injection being controlled atsuch rates as to maintain the relative mobility of said displacementfluid below said minimum total relative mobility at substantially allpoints within said formation.

2. The process of claim 1 wherein said displacement fluid comprises aslug of soluble oil.

3. The process of claim 2 wherein the displacement fluid comprises aslug of soluble oil, followed by a second fluid.

4. The process of claim 3 in which the second fluid contains a majorportion of Water.

5. The process of claim 4 in which the water of the second fluid isthickened by the addition of a thickening agent.

6. The process of claim 5 wherein the thickening agent is selected fromthe group consisting of partially hydrolyzed polyacrylamide, sugar,glycerin, starches carboxymethyl cellulose.

7. The process of claim 3 wherein the petroleum and water are displacedtoward a producing well in said formation.

'8. The process of claim 2 wherein a mobility buifer fluid is injectedafter said displacer fluid, and wherein said mobility butter fluid has alower mobility than said displacement fluid, said mobility beingmeasured at the velocities to be encountered during the displacementprocess.

9. The process of claim 8 wherein the mobility buifer comprises awater-external emulsion.

'10. The process of claim 1 wherein the petroleum and water aredisplaced toward a producing well in said formation.

11. The process of claim 1 wherein a mobility buffer fluid is injectedafter said displacer fluid, and wherein said mobility butfer fluid has alower mobility than said displacement fluid, said mobility beingmeasured at the velocities to be encountered during the displacementprocess.

12. The process of claim 11 wherein the mobility buffer comprises awater-external emulsion.

13. A process for the displacement of residual petroleum frompetroleum-bearing formations from which a portion of the originalpetroleum has been displaced by othr means, said formatoins having atleast one injection means in said formation, said process comprising incom bination the steps of:

(a) determining the relationship between total relative mobility of oiland water relative to water saturation for each of series of samplesreasonably representative of the structure of the formation,

(b) determining the water relative permeability at the zero oil relativepermeability point (or at the existing water saturation of thereservoir) by transient reservoir injectivity tests,

(c) selecting or interpolating from said total relative mobility vs.saturation relationship for said samples, the relationship mostappropriate to the water relative permeability corresponding either tozero oil relative permeability as determined by said injectivity tests,or to the water relative permeability corresponding to the existingwater saturation of the res ervoir,

(d) selecting the minimum mobility from said most appropriaterelationship,

(e) preparing a displacing fluid having a relative mobility not greaterthan said minimum total relative mobility under the conditionsprevailing in the formation, I

(f) injecting said displacement fluid into said at least one injectionmeans so as to displace water and petroleum present in the formation,said injection being controlled at such rates as to maintain therelative mobility of said displacement fluid below said minimum totalrelative mobility at substantially all points in said formation.

14. The process of claim '13 wherein said displacement fluid comprises aslug of soluble oil.

15. The process of claim 14 wherein the displacement fluid comprises aslug of soluble oil, followed by a second fluid.

16. The process of claim 15 in which the second fluid contains a majorportion of Water.

17. The process of claim 16 in which the water of the second fluid isthickened by the addition of a thickening agent.

18. The process of claim .17 wherein the thickening agent is selectedfrom the group consisting of partially hydrolyzed polyacrylamide, sugar,glycerin, starches carboxymethyl cellulose.

19. The process of claim .15 wherein the petroleum and water aredisplaced toward a producing well in said formation.

20. The process of claim 14 wherein a mobility buffer fluid is injectedafter said displacer fluid, and wherein said mobility buffer fluid" hasa lower mobility than said displacement fluid, said mobility beingmeasured at the velocities to be encountered during the displacementprocess.

21. The process of claim 20 wherein the mobility buffer comprises awater-external emulsion.

22. The process of claim 13 wherein the petroleum and water aredisplaced toward a producing well in said formation.

23. The process of claim 13 wherein a mobility buffer fluid is injectedafter said displacer fluid, and wherein said mobility buffer fluid has alower mobility than said displacement fluid, said mobility beingmeasured at the velocities to be encountered during the displacementprocess.

24. The process of claim 23 wherein the mobility buffer comprises awater-external emulsion.

25. A process for the simultaneous displacement of petroleum and waterin formations bearing petroleum and water and having at least oneinjection means in said formation, the improvement comprising:

(a) determining the oil relative permeability relative to watersaturation of at least one rock sample reasonably representative of thestructure of the formation,

(b) determining the water relative permeability in relation to watersaturation of such samples,

() calculating the total relative mobility of water and oil in relationto water saturation for each such samp (d) determining from themobilities of said samples the minimum total relative mobilityreasonably likely to be encountered in the formation,

(e) injecting into said formation a displacement liquid, saiddisplacement liquid having a relative mobility not substantially greaterthan said minimum total relative mobility of oil and water under theconditions prevailing in the formation,

(f) driving a slug of said displacing liquid through said formation withat least one secondary liquid, at least one of said secondary liquidscomprising water, said secondary liquid having a mobility notsubstantially greater than said displacement liquid under substantiallyall of the conditions prevailing during said displacement.

26. A process for the simultaneous displacement of petroleum and waterin formations bearing petroleum and water and having at least oneinjection means in said formation, the improvement comprising:

(a) determining the relationship between total relative mobility of oiland water relative to water saturation 10 for each of a series of rocksamples reasonably representative of the structure of the formation,

(b) determining the water relative permeability at the zero oil relativepermeability point (or at the existing water saturation of thereservoir) by transient reservoir injectivity tests,

(c) selecting or interpolating from said total relative mobility vs.saturation relationships for said samples, the relationship mostappropriate to the water relative permeability corresponding either tozero oil relative permeability as determined by said injectivity tests,or to the water relative permeability corresponding to the existingwater saturation of the reservoir,

(d) determining from the mobilities of said samples the minimum totalrelative mobility reasonably likely to be encountered in the formation,

(e) injecting into said formation a displacement liquid, saiddisplacement liquid having a relative mobility not substantially greaterthan said minimum total relative mobility of oil and water under theconditions prevailing in the formation,

(f) driving a slug of said displacing liquid through said formation withat least one secondary liquid, at least one of said secondary liquidscomprising water, said secondary liquid having a mobility notsubstantially greater than said displacement liquid under substantiallyall of the conditions prevailing during said displacement.

References Cited UNITED STATES PATENTS 3,003,554 10/1961 Craig et al.166-9 3,006,411 10/ 1961 Holbrook 166-9 3,044,544 7/1962 Holbrook et al.166-9 3,148,730 9/1964 Holbert 166-9 3,167,118 1/1965 Habermann 166-93,208,517 9/1965 Binder et a1 166-9 3,221,810 12/1965 Marx 166-9 X3,275,075 9/1966 Gogarty et al. 166-9 3,362,473 1/1968 Foster 166-93,369,601 2/1968 Bond et al 166-9 OTHER REFERENCES Amyx, Bass andWhiting: Petroleum Reservoir Engineering, Physical Properties,McGraw-Hill Book Co., Inc., 1960 (pp. 174-210).

STEPHEN J. NOVOSAD, Primary Examiner.

US. Cl. X.R. 166-9

